A polyimide resin or the like that exhibits excellent heat resistance, electrical properties, mechanical properties, and the like has been used as a material for forming a surface protective film or an interlayer insulating film (interlayer dielectric) of a semiconductor element (device). In recent years, a polybenzoxazole resin that exhibits excellent moisture-proof reliability due to the absence of a carbonyl group derived from a highly polar imide ring has been used for forefront semiconductor elements (devices). A photosensitive resin composition that includes a photosensitive polybenzoxazole resin or a photosensitive polyimide resin, and simplifies the patterning process (i.e., achieves a reduction in process time and an increase in yield) has been developed.
A positive photosensitive resin composition that can be developed using an alkaline aqueous solution has been proposed from the viewpoint of safety. For example, Patent Document 1 discloses a positive photosensitive resin composition that contains a polybenzoxazole precursor resin (i.e., base resin) and a diazoquinone compound (photosensitizer). The positive photosensitive resin composition disclosed in Patent Document 1 exhibits high heat resistance and excellent electrical properties, enables microfabrication, and may be used as a wafer coating material or an interlayer insulating resin composition. The positive photosensitive resin composition utilizes the following development mechanism. The diazoquinone compound present in the unexposed area is insoluble in an alkaline aqueous solution (developer), and interacts with the base resin to implement resistance to the alkaline aqueous solution. The diazoquinone compound becomes soluble in the alkaline aqueous solution upon exposure due to chemical changes, and promotes dissolution of the base resin. The exposed area is dissolved and removed by utilizing the difference in solubility between the exposed area and the unexposed area to obtain a film pattern formed by the unexposed area.
The polybenzoxazole precursor resin included in the positive photosensitive resin composition is dehydrated and cyclized when the polybenzoxazole precursor resin is cured at a high temperature of about 300° C. after forming the film pattern, so that a polybenzoxazole resin that exhibits high heat resistance is obtained. However, the polybenzoxazole resin and the diazoquinone compound are oxidized and decomposed when curing the polybenzoxazole precursor resin, so that the film blackens. A further heat treatment is performed during the semiconductor production process after curing the polybenzoxazole precursor resin. For example, when producing an LOC structure, a lead frame provided with an LOC tape is bonded to a chip at a high temperature of 350 to 450° C. In this case, the polybenzoxazole resin applied to the chip further blackens. A problem (recognition failure) occurs due to discoloration during the subsequent wire bonding step. Therefore, a positive photosensitive resin composition that produces a cured film that has a light color and is discolored to only a small extent even when heated at a high temperature has been desired.
It is important for the positive photosensitive resin composition to exhibit high sensitivity. If the positive photosensitive resin composition exhibits low sensitivity, a decrease in throughput occurs due to an increase in exposure time. When reducing the molecular weight of the base resin in order to improve the sensitivity of the positive photosensitive resin composition, a film loss in the unexposed area may increase during development (i.e., the desired thickness may not be obtained), or the resolution may decrease.
Patent Document 2 discloses a positive photosensitive resin composition that contains a hindered phenol antioxidant having a specific structure, and produces a cured film that has a light color and is discolored to only a small extent due to heating. Patent Document 3 discloses a positive photosensitive resin composition that contains a phenol compound having a specific structure, and exhibits high sensitivity and high resolution.